DE202007014057U1 - Level measuring device for solid containers - Google Patents

Abstract

Level sensor for determining a level, in particular of bulk solids, in a container made of a solid-walled material, wherein the solid-walled material forms a wall, comprising:
a first electrode (103) provided on the wall or within the wall;
a second electrode (103) provided at a predetermined distance from the first capacitor electrode and at the wall or within the wall;
a sensor electronics (110) including a resonant circuit (112), the first electrode and the second electrode being electrically connected to the sensor electronics and electrically isolated from each other; and
a control unit (250), which is suitable for converting a value provided by the sensor electronics into a filling level.

Description

The The invention relates to devices for measuring a level in firm container. In particular, the invention relates Capacitive level sensors for measuring a level in a solid container.

Capacitive level sensors for liquids and fine, ie fine-grained solids are, for example, from the European patent application EP 0338400 or the European patent application EP 0470483 known. The publication EP 0470483 describes, for example, a method for DK compensated capacitive level measurement with a probe assembly having a fill level capacitor and a capacitor for DK compensation that have different capacitive transconductances and that collectively extend over a same level height measurement range. pamphlet EP 0470483 describes that from the measured value of the level measuring probe and the measured value of the compensation probe, a ratio value Q is formed, which depends solely on the dielectric constant ε _r of the filling substance wetting the measuring and compensation probe, and the filling level height H of the filling material is formed from the measured value of the level measuring probe in which the measured value is electronically corrected with a correction value K, which depends on the geometry and the dielectric of the level measuring probe and the ratio Q.

For bulk goods level measuring devices have been developed in the past, for example, in the German utility model DE 20 2006 009 381 are described and allow, in contrast to the above-mentioned documents, a level measurement for bulk materials in an improved manner. For this purpose, rod electrodes are used, which are arranged, for example, within the storage container.

In many technical fields already exist containers, such as silos, which later with a Level monitoring to be equipped. A simple and cost-effective level measurement is here with conventional means often difficult to realize.

Of the present invention is based on the object, a device to provide level measurement, which does not have or at least reduces the aforementioned disadvantages, and cost-effective and easy level measurement for solid silos provides. This task will the devices specified in claims 1 and 20 solved.

advantageous Embodiments emerge from the subclaims, the attached drawings and the description.

According to one Embodiment becomes a level sensor for the determination a level, in particular of bulk materials such as As fuels, in a container of a festwandigen Material, wherein the solid material forms a wall, for Provided. The level sensor includes a first electrode attached to the wall, e.g. B. directly inside or outside the container on the wall or through an adhesive layer or insulation layer connected to the wall, or provided within the wall, one second electrode, which is at a predetermined distance from the first Capacitor electrode and on the wall, z. B. directly inside or outside the container on the wall or through an adhesive layer or insulation layer connected to the wall, or provided within the wall, one a resonant circuit-containing sensor electronics, wherein the first Electrode and the second electrode electrically with the sensor electronics connected and electrically isolated from each other, and a control unit, which is suitable one of the sensor electronics available to convert the adjusted value into a filling level.

According to one Another embodiment is a level monitored Container, z. B. a silo, from a solid material made available. The container includes a wall of solid material; a first electrode, which is provided on the wall or inside the wall is a second electrode that is at a predetermined distance from the first capacitor electrode and on the wall or within the Wall is provided, a resonant circuit including sensor electronics, wherein the first electrode and the second electrode electrically connected to the sensor electronics and electrically isolated from each other, and a control unit, which is suitable one of the sensor electronics available to convert the adjusted value into a filling level.

following Be embodiments of the invention with reference to the drawings shown in a schematic way. Show it:

1a shows a schematic representation of a solid silo with a measuring device, which illustrates embodiments of a device for measuring the level of contents in a silo;

1b shows another side view of 1a ; and

2 illustrates further embodiments of a device for measuring the Fülltandes of contents in a silo.

The embodiments described in the following figures are described with reference to wood pellets as dry bulk materials. However, the invention is not limited thereto. It can be used as bulk materials and natural products such as grain and feed, plastic components, plastic granules, plastic agglomerates, powders, tablets or a variety of other bulk materials. In general, these are substances that are not provided in the form of a liquid. The term "dry" is not limited to the fact that the bulk materials can not have any moisture content The term "dry" refers to the fact that the filling of the container is not or only partially liquid or moist, but in the form of granules, pellets, Brickets or other pieces is introduced into the container. In addition, also pasteuse substances and liquid substances in the container 102 be filled.

1a and 1b show an embodiment of a solid silo with a level measurement. The solid silo has a container 102 made of a hard-walled material, which the container 102 trains. In contrast to previously known capacitive level measuring devices, electrodes for capacitive level measurement are not provided within the container, ie within the silo, in the form of fixed electrodes. The electrodes 103 be on the wall inside the container 102 or mounted outside the container or integrated into the wall material. The electrodes are provided at the edge of the container.

As in 1a and 1b shown are the electrodes 103 with a sensor unit 110 via cable 105 connected. The sensor unit is via a connecting cable 252 with the control unit 250 connected. The electrodes 103 are according to different embodiments of metal bands, a sheet of electrically conductive material, a strand, a metal mesh, a copper strip, a metal foil or other, for. B. thin, flexible and / or flexible electrically conductive tapes provided.

According to embodiments that may be combined with other embodiments described herein, the electrodes may be adhered to the wall of the silo. It is possible, the electrodes from the outside, as in 1b represented, or inside, as in 2 indicated by the dashed lines, to stick to the wall of the silo. In other embodiments, other mounting options may be used. For example, the electrodes may be inserted into a groove on the container wall, screwed or attached by riveting.

By the use of electrodes attached to or in the wall of the silo attached, it is possible to move the space within the Silos completely unmodified to leave and thus one Filling of the silo should not be influenced or impaired. About that In addition, the electrodes can be inside or outside be attached to the wall retrospectively, which is a simple Retrofitting the level measurement allowed. To the For example, metal bands can be inside or outside glued to the wall of the silo.

In this case, the use of electrically conductive electrodes at the edge of the container, within the wall or on the wall means that despite the suitability for the level measurement of bulk solids, a capacitor from the electrodes 103 is formed. In contrast to previously known electrode arrangements of cylinder capacitors or plate capacitors, the capacitors form those of the electrodes 103 in or on the silo housing fixed electrically conductive bands a relatively small capacity. The capacity is up to the filling level 150 (please refer 1b ) of the bulk goods from the capacity with a dielectric constant of the bulk materials (see area 152 ). Above the filling level, an area closes 154 with the dielectric constant of air. Here, the variable component of the capacitance forms only in a part of the space that is not directly between the electrodes. Changing the level changes the capacity of the electrodes 103 existing level capacitor, since the range of the dielectric constant of air and the range of the dielectric constant of the bulk material changes.

According to some embodiments, this arrangement of electrodes may also be used with wall materials having sufficient electrical conductivity to comply with explosion protection regulations. For example, these materials may have electrical conductivity. For example, for metallic walls of the container 102 For example, the electrodes can be coated with an insulating layer or an insulation jacket before being applied to the wall. According to another embodiment that may be combined with other embodiments, an adhesive bond to the wall may provide sufficient insulation to a metallic wall. In the case of metallic silos, the electrodes should be 103 However, be mounted on the inside of the container wall.

According to typical embodiments, the wall of the silo may be made of plastic, glass, ceramic, concrete, plaster or metal. This z. B. wall thicknesses in a range up to 15 mm, z. B. from 1 mm to 15 mm. Typically, with non-metallic containers, an array of electrodes outside the silo can be selected. In the case of metallic silo walls or thick-walled silos, the electrodes can be arranged in the form of metal strips on the inside of the wall of the silo container.

According to others Embodiments, the electrodes can be inside be attached to the wall of the container, or at a Wall thickness of for example less than 15 mm also outside be attached to the container.

According to some embodiments, the electrodes 103 parallel to each other vertically inside or outside along the outer wall of the silo. According to further embodiments, the electrodes may be provided at a parallel distance of about 0.5 cm to about 10 cm, e.g. B. glued, be. In the 2 the electrodes are shown with dashed lines. This illustrates that the electrodes may be disposed within the silo in contact with the tissue or may be incorporated into the wall material itself. According to other embodiments that may be combined with other aspects of the embodiments described herein, the electrodes may also be on the outside of the silo container 102 be upset.

For the embodiments in which the electrodes 103 do not come into contact with the contents, ie if the electrodes are arranged outside the wall of the container, inside or outside in isolated form or possibly even in the wall itself, the level measuring device described herein can also be applied to electrically conductive products or even liquids. In general, embodiments and combinations of embodiments described herein may be used for bulk materials, pastes, or liquids filled into silos.

The arrangement of electrodes given according to the embodiments described herein makes it possible to use them for e.g. As bulk materials and on the other hand, the use of capacitive level measurement in particular for easy retrofitting to existing silos. The resulting low capacity, however, complicates the measurement of the level. The electrodes 103 are with wires 105 with a sensor electronics 110 connected. Due to the difficult level measurement, the wires should be as short as possible, preferably they are shorter than 10 cm or even 3 cm. In addition, to the resonant circuit 112 within the sensor electronics 110 in addition a capacitor 120 provided a stable behavior of the resonant circuit 112 allows.

Of the Oscillation circuit within the sensor electronics can z. B. a Wien-Robinson oscillator be. This is preferably an oscillator which oscillated with a sinusoidal oscillation. A typical frequency of the Oscillating circuit in the empty state of the silo is in the range of 70 to 400 kHz, preferably 100-150 kHz. The frequency decreases itself when the silo is filled.

The electrodes 103 typically have a capacity of 70 to 120 pF / m or 25 to 120 pF / m. The additional capacitor 120 typically has a capacity of 10 to 60 pF, preferably 47 pF or preferably 15 pF. In smaller capacitance embodiments of the capacitor, a higher measurement frequency and thus, for some embodiments, a faster measurement may occur.

When filling the silo 102 The dry bulk material causes dust to form. Therefore, the sensor electronics, which may also be located within the silo, be designed explosion-proof. When dealing with substances that can react with oxygen, eg. As fuels, is expected to explode if inside the silo of the combustible material is present as a fine-grained dust in the air. Since little influence can be exerted on the size and density of the dust grains, in particular when filling the silo, the sensor electronics are designed accordingly for explosion protection. For this purpose, sparks on the electrical components within the potentially explosive atmosphere as well as static charging of ungrounded components and hot surfaces are avoided. Another measure for explosion protection is the above-mentioned conductivity of the silo wall.

Especially when the electrodes 130 attached to the outside of the silo or a passage of the cables 150 from the inside of the silo 102 takes place to the outside, can be a positioning of the sensor electronics 110 also done outside. In this case, even when positioning the sensor electronics outside of the silo 102 a cable length of the cables 105 As will be described in other embodiments, can be achieved. According to typical embodiments, the sensor electronics can be provided inside or outside the container. The control unit 250 is typically outside the container 102 made available.

The output signal of the sensor electronics 110 located oscillator 112 is amplified, and converted to a microcontroller usable signal (square wave, PWM signal or analog signal). The micro-controller measures the frequency and calculates a mean value over the line 252 to a control unit 250 transmitted. According to further embodiments that can be combined with the embodiments described herein, instead of a microcontroller, a field programmable gate array (FPGA) or the like can also be used.

In the control unit, the value determined by the sensor electronics is converted in order to be brought into relation to the size of the silo and / or to the silo form. The control unit includes a CPU and control devices that allow the level z. B. to visualize or further process. Typically, an alarm can be set when falling below a predetermined level. management 252 typically supplies the sensor electronics with voltage and monitors any malfunctions to prevent damage or fire by switching off the sensor electronics in an emergency. The control unit switches the sensor electronics off. The control unit may further include a memory for storing the values. According to a further embodiment, the control unit may also include other display elements such as a screen, as well as controls such as a keyboard or a mouse to allow a more extensive evaluation of the level. As a result, z. For example, an average consumption of the dry bulk or other statistics can be selected, calculated and presented.

According to one In another embodiment, the control unit may substantially also be replaced by a display unit. In this case will from the sensor electronics directly, z. B. a pulse width modulated Signal issued by a display unit in the corresponding Display is implemented. The sensor electronics takes over therefore additional features, so that in terms of the figures described control unit on a display unit can be reduced.

at the initial commissioning or a calibration of the level measurement At another time, the silo is empty and the control unit stores the signal of the sensor electronics in an empty state. about an input device becomes the control unit the shape of the silo and its dimensions supplied in a memory. about a switch can be a menu "silo adjustment when empty" to be selected. This can be a level be defined by 0%. After complete filling of the Silos is through a switch or via an input element a "silo calibration in full condition" is selected. This Value corresponds to the level of 100%. This can the control unit on the silo including its dimensions and the maximum filling height can be adjusted. A corresponding memory unit of the control unit can also change the values save in case of power failure, so that after a power failure no Emptying and refilling is necessary.

According to Further embodiments include a sensor calibration for calibration the filling height possible so that the Plant in empty state is put into operation. While During filling, the system is in operation and measures the values during the filling process. After filling The system can, as described above, by setting the "Siloabgleichs in full condition "and the measured data during filling be calibrated. Here is the control unit and the sensor electronics switched on during the entire filling process and periodically measures the Fill level, thus improved calibration to get during the filling.

The Inventive embodiments have the advantage of being simple and inexpensive for bulk materials or for the Retrofitting a capacitive level measurement can be carried out. The problems that occur here be by an arrangement of the electrodes within the wall or the wall of the silo or in direct contact with the wall of the silo solved within or outside.

According to one another embodiment, with one of the other embodiments can be combined, the sensor contains at least one pair of electrodes connected to sensor electronics. typically, For example, 2, 3, 4 or more pairs of electrodes could be used be provided as capacitor electrodes. Here is a measurement in different areas of the silo possible. According to further embodiments, The multiple pairs can also be equipped with a sensor electronics be connected.

According to yet further embodiments, which may be combined with any of the embodiments described herein, the sensor electronics include means for reducing or preventing static charging of the electrodes. By way of example, pairs of tens diodes and / or resistors are connected to the potential equalization or ground, respectively, by the terminals of the respective electrodes in the sensor electronics. The pairs of diodes are typically connected in series against each other, so that only from a predetermined potential difference between an electrode terminal and the equipotential bonding, for example in the range of 3 V to 12 V, a grounding of An conclusion to prevent static charges. By means of reducing or preventing static charging of the electrodes, the sensor electronics can be protected and further sparking prevented, which is a danger in hazardous areas.

According to Further embodiments include a sensor calibration for calibration the filling height possible so that the Plant in empty state is put into operation. While During filling, the system is in operation and measures the values during the filling process. After filling The system can, as described above, by setting the "Siloabgleichs in full condition "and the measured data during filling be calibrated.

2 illustrates further embodiments. The embodiments sensor electronics and the control unit can be analogous to those in relation to the 1a and 1b illustrated embodiments and combinations thereof be provided. The shape and the properties of the electrodes 103 can also be analogous to the embodiments of the electrodes 103 in the 1a and 1b be made available.

In 2 a larger silo is shown, which has a funnel-shaped lower end. The electrodes 203 are dashed to make it clear that the electrodes are inside the silo 202 or within the silo wall material. At the lower end of the funnel-shaped end, an outlet valve is arranged in order to be able to remove the contents of the silo.

The The above-described embodiments are for illustration of the invention and the invention is not as to this to look restricted.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0338400 [0002]
• - EP 0470483 [0002, 0002, 0002]
• - DE 202006009381 U [0003]

Claims (20)

Level sensor for determining a level, in particular of bulk materials, in a container made of a solid-walled material, wherein the solid-walled material forms a wall, comprising: a first electrode ( 103 ) provided on the wall or inside the wall; a second electrode ( 103 ) provided at a predetermined distance from the first capacitor electrode and at the wall or within the wall; a resonant circuit ( 112 ) containing sensor electronics ( 110 ), wherein the first electrode and the second electrode are electrically connected to the sensor electronics and electrically isolated from each other; and a control unit ( 250 ), which is suitable for converting a value provided by the sensor electronics into a filling level. Fill level sensor according to claim 1, wherein the first and the second electrode at least in one Dimension vertical of at least the maximum level measurement up to at least the minimum level measurement height extend. Level sensor according to a of the preceding claims, wherein the first and second electrodes of a conductive band, preferably of a metal band, particularly preferably consist of a metal foil. Level sensor according to a of the preceding claims, wherein the first and second electrodes are flexible. Level sensor according to a of the preceding claims, wherein the first and second electrodes have a vertical dimension that is at least maximum Level measuring height starting substantially to to an opposite, lower end of the container ranges, preferably from 0 cm to about 5 cm in front of the opposite End of the container is enough. Level sensor according to claim 5, wherein the vertical dimension is designed such that the first and the second electrode is not completely down to the bottom End of the container is formed. Level sensor according to a of the preceding claims, wherein the first and second electrodes are formed substantially parallel to each other. A level sensor according to claim 7, wherein the first and second electrodes ( 103 ) are mounted at a distance of at least 3 mm, preferably at a distance of 0.5 cm to 20 cm, particularly preferably at a distance of 1 cm to 10 cm. Level sensor according to a of the preceding claims, wherein the solid-walled material is plastic, Ceramic or glass is. Level sensor according to a of the preceding claims, wherein the first and second electrodes stuck in the solid-walled material or embedded in the wall are. Level sensor according to a of the preceding claims, wherein the first and second electrodes with an insulating layer at least between the wall and the each electrode is formed. Level sensor according to a of the preceding claims, wherein the first and second electrodes within the container adjacent to the wall or outside container adjacent to the wall are placed. Level sensor according to a of the preceding claims, wherein the sensor electronics inside the container and the control unit outside the container is arranged. Level sensor according to one of the preceding claims, wherein the first and the second electrode ( 103 ) form a capacitor with a capacity per unit length of a maximum of 120 pF / m. Level sensor according to one of the preceding claims, wherein the sensor electronics includes a resonant circuit, preferably a Wien-Robinson-Ozillator, and in addition a capacitor ( 120 ) having a capacity of about 10 pF to 75 pF, preferably about 45 to 55 pF, in parallel. Level sensor according to a of the preceding claims, wherein the resonant circuit and the sensor electronics is suitable, a capacity change in the range 2-6 pF or 1-6 pF. Level sensor according to a of the preceding claims, wherein the sensor electronics is designed explosion-proof. Level sensor according to one of the preceding claims, wherein the first and the second electrode each with an electrical conductor ( 105 ) are connected to the sensor electronics and wherein the electrical conductors have a maximum length of 30 cm, preferably 20 cm, more preferably about 5 cm. Level sensor according to one of the preceding claims, wherein the first and the second electrode ( 102 ) are made of metal. Level monitored container made of a solid material containing containers: A Wall made of a hard-walled material; a level sensor according to one of the preceding claims.